This invention relates to a method and apparatus for aligning and retaining ophthalmic lenses during a blocking operation.
In ophthalmic optics, toric lens blanks are formed from glass or plastic compositions. A convex surface of the lens blank is then mounted upon a retaining member known as a lens block which is preferably composed of a low melting temperature alloy. In general terms finishing of the lens blank is achieved by mounting the lens and block accurately upon a tool holding assembly whereupon prescriptive surfaces are ground into the lens blank with one prescriptive value for the horizontal meridian or base cut and a different prescriptive value for the vertical meridian or cylinder cut. Following the initial step of grinding, the lens is mounted upon further process machinery which serves to lap and polish a final prescription onto the lens blank. Finally, the lens blank is mounted upon an edge grinding apparatus and an edge configuration is ground upon the lens to achieve proper fit of the lens into conventional eyeglass frames.
In each of the foregoing process steps, it is critical to maintain a desired orientation and reference of the lens being ground. This is achieved by accurately mounting the lens upon the lens block.
In the past, lens blanks to be mounted or blocked have been fitted upon frame assemblies and molten alloy has been injected into a cavity surrounding a central convex portion of the lens blank. Upon cooling of the molten metal, the lens is removed from the blocking apparatus for further processing as discussed above. Examples of prior lens blocking methods and apparatus may be had by reference to U.S. Suddarth Pat. No. 3,468,366; Saroffen Pat. No. 3,704,558 and Coburn et al. U.S. Pat. No. 3,794,314, of common assignment with the subject application. These patents disclosed various advantageous methods and apparatus for blocking an ophthalmic lens.
Notwithstanding the advantages provided by prior art lens blocking techniques, room for improvement remains. In this connection, it would be highly desirable to provide a method and apparatus for aligning a lens blank prior to a lens blocking operation wherein orientation of the base and cylinder axes may be quickly and accurately achieved with a minimum of parallax error. Still further, it would be desirable to provide a lens retaining apparatus which may be quickly positioned upon an aligned lens with uniform pressure which will not deflect or bend lens blanks, such as those composed of plastic compositions.